Control of corrosion by molten salts

Abstract

A molten halide salt mixture for use in a nuclear fission reactor. The molten halide salt mixture comprises a reactive metal halide salt. The reactive metal halide salt is a halide salt of a reactive metal. The reactive metal has a Pauling electronegativity of at least 1.2, and at least one other halide salt of higher valence than the reactive metal halide salt. The reactive metal salt is at a concentration sufficient to prevent corrosion of metals in contact with the molten halide salt mixture and insufficient to cause deposition of the reactive metal at an operating temperature of the nuclear fission reactor.

1 . A molten halide salt mixture for use in a nuclear fission reactor, the molten halide salt mixture comprising a reactive metal halide salt, wherein the reactive metal halide salt is a halide salt of a reactive metal, the reactive metal having:
 a Pauling electronegativity between 1.2 and 1.7, and   at least one other halide salt of higher valence than the reactive metal halide salt and wherein the reactive metal salt is at a concentration sufficient to prevent corrosion of metals in contact with the molten halide salt mixture and insufficient to cause deposition of the reactive metal at an operating temperature of the nuclear fission reactor.   
     
     
         2 . A molten halide salt mixture according to  claim 1 , wherein the reactive metal halide salt is a monovalent or divalent halide salt of titanium, zirconium, or vanadium. 
     
     
         3 . A molten halide salt mixture according to  claim 2 , wherein the reactive metal halide salt is one of:
 zirconium monochloride;   zirconium difluoride;   titanium difluoride;   vanadium difuoride.   
     
     
         4 . A molten halide salt mixture according to  claim 1 , wherein the molten salt is for use as one of:
 a fissile fuel;   a coolant salt.   
     
     
         5 . A molten halide salt mixture according to  claim 1 , wherein the concentration of reactive metal halide salt is between 0.1% and 2%. 
     
     
         6 . A molten halide salt mixture according to  claim 1 , wherein the molten halide salt mixture further comprises a further halide salt of the reactive metal having a higher valence than the reactive metal halide salt. 
     
     
         7 . A nuclear fission reactor comprising a molten halide salt fissile fuel, wherein the molten halide salt fissile fuel is a molten halide salt mixture according to  claim 1 . 
     
     
         8 . A nuclear fission reactor comprising a molten halide salt coolant, wherein the molten halide salt coolant is a molten halide salt mixture according to  claim 1 . 
     
     
         9 . A nuclear fission reactor according to  claim 8 , and comprising a region of molten salt halide coolant at a lower temperature than other regions of the molten halide salt coolant, and a solid piece of the reactive metal contacting the molten halide salt coolant within that region. 
     
     
         10 . A nuclear fission reactor according to  claim 8 , and comprising a sensor configured to monitor a concentration of the reactive metal halide salt in the molten halide salt coolant, and a reactive metal halide salt source configured to introduce additional reactive metal halide salt to the molten halide salt coolant if the concentration falls below a predefined threshold. 
     
     
         11 . A nuclear fission reactor according to  claim 10 , wherein the reactive metal halide salt source is configured to introduce additional reactive metal halide salt to the molten halide salt coolant by intermittently contacting the molten halide salt coolant with the reactive metal. 
     
     
         12 . A method of reducing corrosion of metals by a molten halide salt mixture, the method comprising including a reactive metal halide salt, wherein the reactive metal halide salt is a halide salt of a reactive metal, the reactive metal having:
 a Pauling electronegativity between 1.2 and 1.7, and   at least one other halide salt of higher valence than the reactive metal halide salt and wherein the reactive metal salt is at a concentration sufficient to prevent corrosion of metals in contact with the molten halide salt mixture and insufficient to cause deposition of the reactive metal at an operating temperature of the nuclear fission reactor.   
     
     
         13 . A method according to  claim 12 , wherein the reactive metal halide salt is zirconium difluoride. 
     
     
         14 . A method according to  claim 12 , wherein the reactive metal halide salt is zirconium monochloride. 
     
     
         15 . A method according to  claim 12 , wherein introducing the reactive metal halide salt comprises contacting the molten halide salt mixture with the reactive metal in a region at a lower temperature than other regions of the molten halide salt. 
     
     
         16 . A method according to  claim 12 , wherein introducing the reactive metal halide salt comprises intermittently contacting the molten halide salt mixture with the reactive metal. 
     
     
         17 . A method according to  claim 12 , and comprising monitoring a concentration of the reactive metal halide salt in the molten halide salt mixture, and introducing additional reactive metal halide salt to the molten halide salt mixture if the concentration falls below a predetermined threshold. 
     
     
         18 . A method according to  claim 12 , and comprising using the molten halide salt mixture in a nuclear fission reactor as one of:
 a fissile fuel;   a coolant salt.   
     
     
         19 . A method according to  claim 12 , wherein the concentration of reactive metal halide salt is between 0.1% and 2%. 
     
     
         20 . A method according to  claim 12 , wherein the molten halide salt mixture further comprises a further halide salt of the reactive metal having a higher valence than the reactive metal halide salt.